Light emitter for a display

ABSTRACT

There is provided a light emitter for a display comprising a photoalignment layer; and photoaligned on said photoalignment layer, a light emitting polymer. Also provided are methods for forming the light emitter and the use of the light emitter in displays, backlights, electronic apparatus and security viewers.

This application is a continuation-in-part of Ser. No. 09/898,518 filedJul. 3, 2001 and claims priority from GB Application No. 0115984.7 filedJun. 29, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light emitter for a display for usein electronic products and a method of forming the light emitter anddisplay.

2. Prior Art

Modern consumer electronics require cheap, high-contrast displays withgood power efficiency and low drive voltages. Particular applicationsinclude displays for mobile phones and hand-held computers.

Conventional displays comprise twisted nematic liquid crystal displays(TN-LCDs) with active matrix addressing and super-twisted nematic liquidcrystal displays (STN-LCDs) with multiplex addressing. These howeverrequire intense back lighting which presents a heavy drain on power. Thelow intrinsic brightness of LCDs is believed to be due to high losses oflight caused by the absorbing polarizers and filters which can result inexternal transmission efficiencies of as low as 4%.

SUMMARY OF THE INVENTION

The Applicants have now devised a new kind of light emitter for adisplay which offers the prospect of lower power consumption and/orhigher brightness. The display utilises an alternative light sourcewhich can in embodiments be used instead of the conventional polarizersand/or back light. The alternative light source comprises a lightemitting polymer or polymer network aligned on a photoalignment layer.The combination of this alternative lighting source with existing LCDtechnology offers the possibility of low-cost, bright, portable displayswith the benefits of simple manufacturing and enhanced power efficiency.

According to one aspect of the present invention there is provided alight emitter for a display comprising a photoalignment layer; andaligned on said photoalignment layer, a light emitting polymer.

The photoalignment layer is comprised of materials that photoalign (e.g.by cross-linking) to form anisotropic layers when polarised light (e.g.UV) is applied.

The photoalignment layer typically comprises a chromophore attached to asidechain polymer backbone by a flexible spacer entity. Suitablechromophores include cinnamates or coumarins, including derivatives of 6or 7-hydroxycoumarins. Suitable flexible spacers comprise unsaturatedorganic chains, including e.g. aliphatic, amine or ether linkages.

An exemplary photoalignment layer comprises the 7-hydroxycoumarincompound having the formula:

Other suitable materials for use in photoalignment layers are describedin M. O'Neill and S. M. Kelly, J. Phys. D. Appl. Phys. [2000], 33, R67.

In aspects, the photoalignment layer is photocurable. This allows forflexibility in the angle at which the light emitting polymer (e.g. as aliquid crystal) is alignable and thus flexibility in its polarizationcharacteristics.

The photalignment layer may also be doped with a hole transportcompound, that is to say a compound which enables hole transport withinthe photoalignment layer such as a triarylamine. Examples of suitabletriarylamines include those described in C. H. Chen, J. Shi, C. W. Tang,Macromol Symp. [1997] 125, 1.

An exemplary hole transport compound is4,4′,4″-tris[N-(1-napthyl)-N-phenyl-amino]triphenylamine which has theformula:

In aspects, the hole transport compound has a tetrahedral (pyramidal)shape which acts such as to controllably disrupt the alignmentcharacteristics of the layer.

In one aspect, the photoalignment layer includes a copolymerincorporating both linear rod-like hole-transporting and photoactiveside chains.

Suitably, the light emitting polymer is a polymer having a lightemitting chromophore. Suitable chromophores include fluorene,vinylenephenylene, anthracene and perylene. Useful chromophores aredescribed in A. Kraft, A. C. Grimsdale and A. B. Holmes, Angew. Chem.Int. Ed. Eng. [1998], 37, 402.

Suitably, the light emitting polymer is a liquid crystal which can bealigned to emit polarised light. A suitable class of polymers is basedon fluorene.

In one aspect, the light emitting polymer comprises an organic lightemitting diode (OLED) such as described in S. M. Kelly, Flat PanelDisplays: Advanced Organic Materials, RSC Materials Monograph, ed. J. A.Connor, [2000]; C. H. Chen, J. Shi, C. W. Tang, Macromol Symp. [1997]125, 1; R. H. Friend, R. W. Gymer, A. B. Holmes, J. H. Burroughes, R. N.Marks, C. Taliani, D. D. C. Bradley, D. A. Dos Santos, J. L. Bredas, M.Logdlund, W. R. Salaneck, Nature [1999] 397, 121; M. Grell, D. D. C.Bradley, Adv. Mater. [1999] 11, 895; N. C. Greenman, R. H. Friend SolidState Phys. [1995] 49, 1.

OLEDs may be configured to provide polarized electroluminescence.

The reactive mesogen (monomer) typically has a molecular weight of from400 to 2,000. Lower molecular weight monomers are preferred becausetheir viscosity is also lower leading to enhanced spin coatingcharacteristics and shorter annealing times which aids processing. Thelight emitting polymer typically has a molecular weight of above 4,000,typically 4,000 to 15,000.

The light emitting polymer typically comprises from 5 to 50, preferablyfrom 10 to 30 monomeric units.

The light emitting polymer is aligned on the photoalignment layer.Suitably, the photoaligned polymer comprises uniaxially alignedchromophores. Typically light polarization ratios of 30 to 40 arerequired, but with the use of a clean up polarizer ratios of 10 or morecan be adequate for display uses.

In aspects, the light emitting polymer is formed by a polymerizationprocess. Suitable processes involve the polymerization of reactivemesogens (e.g. in liquid crystal form) via photo-polymerization orthermal polymerization of suitable end-groups of the mesogens. Inpreferred aspects, the polymerization process results in cross-linkinge.g. to form an insoluble, cross-linked network.

The polymerization process can in a preferred aspect be conducted insitu after deposition of the reactive mesogens on the photoalignmentlayer by any suitable deposition process including a spin-coatingprocess.

In a preferred polymerization process, the light emitting polymer isformed by photopolymerization of reactive mesogens having photoactiveend-groups.

Suitable reactive mesogens have the following general structure:B-S-A-S-B  (general formula 1)wherein

A is a chromophore;

S is a spacer; and

B is an endgroup which is susceptible to radical photopolymerisation.

The polymerisation typically results in a light emitting polymercomprising arrangements of chromophores (e.g. uniaxially aligned) spacedby a crosslinked polymer backbone. The process is shown schematically inFIG. 1 from which it may be seen that the polymerisation of reactivemonomer 10 results in the formation of crosslinked polymer network 20comprising crosslink 22, polymer backbone 24 and spacer 26 elements.

Suitable chromophore (A) groups have been described previously.

Suitable spacer (S) groups comprise organic chains (e.g. unsaturated),including e.g. flexible aliphatic, amine or ether linkages. Aliphaticspacers are preferred. The presence of spacer groups aids the solubilityand lowers the melting point of the light emitting polymer which assiststhe spin coating thereof.

Suitable endgroups are susceptible to photopolymerization (e.g. by aprocess using UV radiation, generally unpolarized). Preferably, thepolymerization involves cyclopolymerization (i.e. the radicalpolymerization step results in formation of a cyclic entity).

A typical polymerization process involves exposure of a reactive mesogenof general formula 1 to UV radiation to form an initial radical havingthe general formula as shown below:B-S-A-S-B.  (general formula 2)wherein A, S and B are as defined previously and B. is a radicalisedendgroup which is capable of reacting with another B endgroup(particularly to form a cyclic entity). The B. radicalised endgroupsuitably comprises a bound radical such that the polymerisation processmay be sterically controlled.

Suitable endgroups include dienes such as 1,4, 1,5 and 1,6 dienes. Thediene functionalities may be separated by aliphatic linkages, but otherinert linkages including ether and amine linkages may also be employed.

Methacrylate endgroups have been found to be less suitable than dienesbecause the high reactivity of the radicals formed after thephotoinitiation step can result in a correspondingly highphotodegradation rate. By contrast, it has been found that thephotodegradation rate of light emitting polymers formed from dienes ismuch lower. The use of methacrylate endgroups also does not result incyclopolymerization.

Where the endgroups are dienes the reaction typically involvescyclopolymerization by a sequential intramolecular and intermolecularpropagation: A ring structure is formed first by reaction of the freeradical with the second double bond of the diene group. A double ring isobtained by the cyclopolymerization which provides a particularly rigidbackbone. The reaction is in general, sterically controlled.

Suitable reactive mesogens have the general formula:

wherein R has the general formula: X-S2-Y-Z

-   and wherein-   X=O, CH₂ or NH and preferably X=O;-   S2=linear or branched alkyl or alkenyl chain optionally including a    heteroatom (e.g. O, S or NH) and preferably S2=a linear alkyl chain;-   Y=O, CO₂ or S and preferably Y=CO₂; and-   Z=a diene (end-group) and preferably Z=a 1,4, 1,5 or 1,6 diene.

Exemplary reactive mesogens have the general formula:

wherein R is:

An exemplary reactive mesogen has the formula:

All of Compounds 3 to 6 exhibit a nematic phase with a clearing point(N—I) between 79 and 120° C.

Other suitable exemplary reactive mesogens have the general formula:

wherein n is from 2 to 10, preferably from 3 to 8 and wherein, as above,R has the general formula: X-S2-Y-Z

-   and wherein-   X=O, CH₂ or NH and preferably X=O;-   S2=linear or branched alkyl or alkenyl chain optionally including a    heteroatom (e.g. O, S or NH) and preferably S2=a linear alkyl chain;-   Y=O, CO₂ or S and preferably Y=CO₂; and-   Z=a diene (end-group) and preferably Z=a 1,4, 1,5 or 1,6 diene.

Suitably, R is as for any of Compounds 3 to 6, as shown above.

A particular class of exemplary reactive mesogens has the formula:

wherein:

-   n is from 2 to 10, preferably from 3 to 8; and-   m is from 4 to 12, preferably from 5 to 11.

Still further suitable exemplary reactive mesogens have the generalformula:

-   wherein A=H or F-   and wherein, as above, R has the general formula: X-S2-Y-Z-   and wherein-   X=O, CH₂ or NH and preferably X=O;-   S2=linear or branched alkyl or alkenyl chain optionally including a    heteroatom (e.g. O, S or NH) and preferably S2=a linear alkyl chain;-   Y=O, CO₂ or S and preferably Y=CO₂; and-   Z=a diene (end-group) and preferably Z=a 1,4, 1,5 or 1,6 diene.

Suitably, R is as for any of Compounds 3 to 6, as shown above.

Particular exemplary reactive mesogens of this type have the formula:

In aspects, the preferred photopolymerization process can be conductedat room temperature, thereby minimizing any possible thermal degradationof the reactive mesogen or polymer entities. Photopolymerization is alsopreferable to thermal polymerization because it allows subsequentsub-pixellation of the formed polymer by lithographic means.

Further steps may be conducted prior to the polymerization processincluding doping of the reactive mesogen. The dopant may in aspectscomprise a further reactive monomer capable of co-polymerization withthe reactive mesogen.

Further steps also may be conducted subsequent to the polymerizationprocess including doping and the addition of other layers (as describedin more detail below).

The light emitting polymer may be aligned by a range of methodsincluding mechanical stretching, rubbing, and Langmuir-Blodgettdeposition. Mechanical alignment methods can however lead to structuraldegradation. The use of rubbed polyimide is a suitable method foraligning the light emitting polymer especially in the liquid crystalstate. However, standard polyimide alignment layers are insulators,giving rise to low charge injection for OLEDs.

The susceptibility to damage of the alignment layer during the alignmentprocess can be reduced by the use of a non-contact photoalignmentmethod. In such methods, illumination with polarized light introduces asurface anisotropy to the alignment layer and hence a preferred in-planeorientation to the overlying light emitting polymer (e.g. in liquidcrystal form).

The aligned light emitting polymer is in one aspect in the form of aninsoluble nematic polymer network. Cross-linking has been found toimprove the photoluminescence properties.

M. O'Neill, S. M. Kelly J. Appl. Phys. D [2000] 33, R67 provides areview of photalignment materials and methods.

The emitter herein may include additional layers such as carriertransport layers. The presence of an electron-transporting polymer layer(e.g. comprising an oxadiazole ring) has been found to increaseelectroluminescence.

An exemplary electron transporting polymer has the formula:

Pixellation of the light emitter may be achieved by selectivephotopatterning to produce red, green and blue pixels as desired. Thepixels are typically rectangular in shape. The pixels typically have asize of from 1 to 50° μm. For microdisplays the pixel size is likely tobe from 1 to 50 μm, preferably from 5 to 15 μm, such as from 8 to 10 μm.For other displays, larger pixel sixes e.g. 300 μm are more suitable.

In one preferred aspect, the pixels are arranged for polarized lightemission. Suitably, the pixels are of the same color but have theirpolarization direction in different orientations. To the naked eye thiswould look one color, but when viewed through a polarizer some pixelswould be bright and others less bright thereby giving an impression of3D viewing when viewed with glasses having a different polarization foreach eye.

The layers may also be doped with photoactive dyes. In aspects, the dyecomprises a dichroic or pleachroic dye. Examples include anthraquinonedyes or tetralines, including those described in S. M. Kelly, Flat PanelDisplays: Advanced Organic Materials, RSC Materials Monograph, ed. J. A.Connor, [2000]. Different dopant types can be used to obtain differentpixel colors.

Pixel color can also be influenced by the choice of chromophore withdifferent chromophores having more suitability as red, green or bluepixels, for example using suitably modified anthraquinone dyes.

Multicolor emitters are envisaged herein comprising arrangements orsequences of different pixel colors.

One suitable multicolor emitter comprises stripes of red, green and bluepixels having the same polarization state. This may be used as asequential color backlight for a display which allows the sequentialflashing of red, green and blue lights. Such backlights can be used intransmissive and reflective FLC displays where the FLC acts as a shutterfor the flashing colored lights.

Another suitable multicolor emitter comprises a full color pixelateddisplay in which the component pixels thereof have the same or differentalignment.

Suitable multicolor emitters may be formed by a sequential ‘coat,selective cure, wash off’ process in which a first color emitter isapplied to the aligned layer by a suitable coating process (e.g. spincoating). The coated first color emitter is then selectively cured onlywhere pixels of that color are required. The residue (of uncured firstcolor emitter) is then washed off. A second color emitter is thenapplied to the aligned layer, cured only where pixels of that color arerequired and the residue washed off. If desired, a third color may beapplied by repeating the process for the third color.

The above process may be used to form a pixelated display such as foruse in a color emissive display. This process is simpler thantraditional printing (e.g. ink jet) methods of forming such displays.

According to another aspect of the present invention there is provided abacklight for a display comprising a power input; and a light emitter asdescribed hereinbefore.

The backlight may be arranged for use with a liquid crystal display. Inaspects, the backlight may be monochrome or multicolor.

According to yet another aspect of the present invention there isprovided a display comprising a screen; and a light emitter or backlightas described hereinbefore.

The screen may have any suitable shape or configuration including flator curved and may comprise any suitable material such as glass or aplastic polymer.

The light source of the present invention has been found to beparticularly suitable for use with screens comprising plastic polymerssuch as polyethylene or polyethylene terephthalate (PET).

The display is suitable for use in electronic apparatus including adrive means therefor. The display is suitable for use in consumerelectronic goods such as mobile telephones, hand-held computers, watchesand clocks and games machines.

According to yet another aspect of the claimed invention there isprovided a security viewer (e.g. in kit form) comprising a light emitteras described herein in which the pixels are arranged for polarizedemission; and view glasses having a different polarization for each eye.

According to yet another aspect of the claimed invention there isprovided a 3D viewer (e.g. in kit form) comprising a light emitter asdescribed herein in which the pixels are arranged for polarized emissionwherein the alignment of polarisation axis of each pixel is different;and a viewer having polarization characteristics aligned with those ofthe pixels.

According to yet another aspect of the claimed invention there isprovided a method of forming a light emitter for a display comprisingforming a photoalignment layer; and aligning a light emitting polymer onsaid photoalignment layer.

According to yet another aspect of the claimed invention there isprovided a method of forming a multicolor emitter comprising applying afirst color light emitter to the photoalignment layer; selectivelycuring said first color light emitter only where that color is required;washing off any residue of uncured first color emitter; and repeatingthe process for a second and any subsequent light color emitters.

All references herein are incorporated by reference in their entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of systems according to the invention will now be describedwith reference to the accompanying experimental detail and drawings inwhich:

FIG. 1 is a schematic representation of a polymerization process herein;

FIG. 2 is a representation of a display device in accord with thepresent invention;

FIG. 3 is a representation of a backlight in accord with the presentinvention; and

FIG. 4 is a representation of a polarised sequential light emittingbacklight in accord with the present invention.

FIGS. 5 to 12 show reaction schemes 1 to 8, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS General ExperimentalDetails

Fluorene, 2-(tributylstanyl)thiophene, 4-(methoxyphenyl)boronic acid andthe dienes were purchased from Aldrich and used as received. Reagentgrade solvents were dried and purified as follows. N,N-Dimethylformamide(DMF) was dried over anhydrous P₂O₅ and purified by distillation.Butanone and methanol were distilled and stored over 5 Å molecularsieves. Triethylamine was distilled over potassium hydroxide pellets andthen stored over 5 Å molecular sieves. Dichloromethane was dried bydistillation over phosphorus pentoxide and then stored over 5 Åmolecular sieves. Chloroform was alumina-filtered to remove any residualethanol and then stored over 5 Å molecular sieves. ¹H nuclear magneticresonance (NMR) spectra were obtained using a JOEL JMN-GX270 FT nuclearresonance spectrometer. Infra-red (IR) spectra were recorded using aPerkin Elmer 783 infra-red spectrophotometer. Mass spectral data wereobtained using a Finnegan MAT 1020 automated GC/MS. The purity of thereaction intermediates was checked using a CHROMPACK CP 9001 capillarygas chromatograph fitted with a 10 m CP-SIL 5CB capillary column. Thepurity of the final products was determined by high-performance liquidchromatography [HPLC] (5 □m, 25 cm×0.46 cm, ODS Microsorb column,methanol, >99%) and by gel-permeation chromatography [GPC] (5 □m, 30cm×0.75 cm, 2× mixed D PL columns, calibrated using polystyrenestandards [molecular weights=1000-4305000], toluene; no monomerpresent). The polymers were found to exhibit moderate to high M_(w)values (10,000-30,000) and acceptable M_(w)/M_(n) values (1.5-3). Theliquid crystalline transition temperatures were determined using anOlympus BH-2 polarising light microscope together with a Mettler FP52heating stage and a Mettler FP5 temperature control unit. The thermalanalysis of the photopolymerisable monomers (Compounds 3 to 6) and themainchain polymer (Compound 7) was carried out by a Perkin-ElmerPerkin-Elmer DSC 7 differential scanning calorimeter in conjunction witha TAC 7/3 instrument controller. Purification of intermediates andproducts was mainly accomplished by column chromatography using silicagel 60 (200-400 mesh) or aluminium oxide (Activated, Brockman 1; ˜150mesh). Dry flash column chromatography was carried out using silica gelH (Fluka, 5-40 μm). Electroluminescent materials were further purifiedby passing through a column consisting of a layer of basic alumina, athin layer of activated charcoal, a layer of neutral alumina and a layerof Hi-Flo filter aid using DCM as an eluent. This was followed byrecrystallisation from an ethanol-DCM mixture. At this stage, allglass-wear was thoroughly cleaned by rinsing with chromic acid followedby distilled water and then drying in an oven at 100° C. for 45 minutes.Purity of final products was normally confirmed by elemental analysisusing a Fisons EA 1108 CHN apparatus.

Key intermediate 1:2,7-bis[5-(4-hydroxyphenyl)thien-2-yl]-9,9-dipropylfluorene wassynthesised as shown in Reaction Scheme 1. Full details each step arenow given:

9-Propylfluorene: A solution of n-Butyllithium (18.0 cm³, 10M solutionin hexanes, 0.18 mol) was added slowly to a solution of fluorene (30.0g, 0.18 mol) in THF (350 cm³) at −50° C. The solution was stirred for 1h at −75° C. and 1-bromopropane (23.0 g, 0.19 mol) was added slowly. Thesolution was allowed to warm to RT and then stirred for a further 1 h.Dilute hydrochloric acid (100 cm³, 20%) and water (100 cm³) were addedand the product extracted into diethyl ether (3×150 cm³). The etherealextracts were dried (MgSO₄) and concentrated to a pale yellow oil (37.5g, yield 100%): Purity 100% (GC).

¹H NMR (CD₂Cl₂) δ: 7.75 (2H, dd), 7.52 (2H, m), 7.32 (4H, m), 3.98 (1H,t), 1.95 (2H, m), 1.19 (2H, m), 0.85 (3H, t). IR (KBr pellet cm⁻¹): 3070(m), 2962 (s), 1450 (s), 1296 (w), 1189 (w), 1030 (w), 938 (w), 739 (s).MS (m/z): 208 (M⁺), 178, 165 (M100), 139.

9,9-Dipropylfluorene: A solution of n-Butyllithium (29.0 cm³, 2.5Msolution in hexanes, 0.073 mol) was added slowly to a solution of9-propylfluorene (15.0 g, 0.072 mol) in THF at −50° C. The solution wasstirred for 1 h at −75° C., 1-bromopropane (10.0 g, 0.092 mol) was addedslowly and the temperature raised to RT after completion of theaddition. After 18 h, dilute hydrochloric acid (20%, 100 cm³) and water(100 cm³) were added and the product extracted into diethyl ether (2□100 cm³). The ethereal extracts were dried (MgSO₄) and concentrated toa pale brown oil which crystallised overnight at RT. The product waspurified by recrystallisation from methanol to yield a white crystallinesolid (14.5 g, yield 80%) mp 47-49° C. (Lit. 49-50° C. ¹⁹). Purity 100%(GC).

¹H NMR (CDCl₃) δ: 7.68 (2H, m), 7.31 (6H, m), 1.95 (4H, t), 0.65 (10H,m). IR (KBr pellet cm−1): 3068 (m), 2961 (s), 1449 (s), 1293 (w), 1106(w), 1027 (w), 775 (m), 736 (s), 637 (m). MS (m/z): 250 (M⁺), 207(M100), 191, 179, 165.

2,7-Dibromo-9,9-dipropylfluorene: Bromine (10.0 g, 0.063 mol) was addedto a stirred solution of 9,9-dipropylfluorene (7.0 g, 0.028 mol) inchloroform (25 cm³) and the solution purged with dry N₂ for 0.5 h.Chloroform (50 cm³) was added and the solution washed with saturatedsodium bisulphite solution (75 cm³), water (75 cm³), dried (MgSO₄) andconcentrated to a pale yellow powder (11.3 g, yield 98%) mp 134-137° C.

¹H NMR (CDCl₃) δ: 7.51 (2H, d), 7.45 (4H, m), 1.90 (4H, t), 0.66 (10H,m). IR (KBr pellet cm⁻¹): 2954 (s), 1574 (w), 1451 (s), 1416 (m), 1270(w), 1238 (w), 1111 (w), 1057 (s), 1006 (w), 931 (w), 878 (m), 808 (s),749 (m). MS (m/z): 409 (M⁺), 365, 336, 323, 284, 269, 256, 248, 202,189, 176 (M100), 163.

2,7-bis(Thien-2-yl)-9,9-dipropylfluorene: A mixture of2,7-dibromo-9,9-dipropylfluorene (6.0 g, 0.015 mol),2-(tributylstannyl)thiophene (13.0 g, 0.035 mol) andtetrakis(triphenylphosphine)-palladium (0) (0.3 g, 2.6×10⁻⁴ mol) in DMF(30 cm³) was heated at 90° C. for 24 h. DCM (200 cm³) was added to thecooled reaction mixture and the solution washed with dilute hydrochloricacid (2□150 cm³, 20%), water (100 cm³), dried (MgSO₄) and concentratedonto silica gel for purification by column chromatography [silica gel,DCM:hexane 1:1]. The compound was purified by recrystallisation fromDCM: ethanol to yield light green crystals (4.3 g, yield 6 9%), mp165-170° C. Purity 100% (GC).

¹H NMR (CDCl₃) δ: 7.67 (2H, d), 7.60 (2H, dd), 7.57 (2 h, d), 7.39 (2H,dd), 7.29 (2H, dd), 7.11 (2H, dd), 2.01 (4H, m), 0.70 (10H, m). IR (KBrpellet cm⁻¹): 2962 (m), 2934 (m), 2872 (m), 1467 (m), 1276 (w), 1210(m), 1052 (w), 853 (m), 817 (s), 691 (s). MS (m/z): 414 (M⁺, M100), 371,342, 329, 297, 207, 165.

2,7-bis(5-Bromothien-2-yl)-9,9-dipropylfluorene: N-Bromosuccinimide (2.1g, 0.012 mol freshly purified by recrystallisation from water) was addedslowly to a stirred solution of 2,7-bis(thien-2-yl)-9,9-dipropylfluorene(2.3 g, 5.55×10⁻³ mol) in chloroform (25.0 cm³) and glacial acetic acid(25.0 cm³). The solution was heated under reflux for 1 h, DCM (100 cm³)added to the cooled reaction mixture, washed with water (100 cm³), HCl(150 cm³, 20%), saturated aqueous sodium bisulphite solution (50 cm³),and dried (MgSO₄). The solvent was removed in vacuo and the productpurified by recrystallisation from an ethanol-DCM mixture to yieldyellow-green crystals (2.74 g, yield 86%). mp 160-165° C.

¹H NMR (CDCl₃) δ: 7.66 (2H, d), 7.49 (2H, dd), 7.46 (2H, d), 7.12 (2H,d), 7.05 (2H, d), 1.98 (4H, t), 0.69 (10H, m). IR (KBr pellet cm⁻¹):3481 (w), 2956 (s), 1468 (s), 1444 (m), 1206 (w), 1011 (w), 963 (w), 822(m), 791 (s), 474 (w). MS (m/z): 572 (M⁺), 529, 500, 487, 448, 433, 420,407, 375, 250,126.

2,7-bis[5-(4-Methoxyphenyl)thien-2-yl]-9,9-dipropylfluorene: A mixtureof 2,7-bis(5-bromothien-2-yl)-9,9-dipropylfluorene (2.7 g, 4.7×10⁻³mol), 4-(methoxyphenyl)boronic acid (2.15 g, 0.014 mol),tetrakis(triphenylphosphine)palladium (0) (0.33 g, 2.9×10⁻⁴ mol), sodiumcarbonate (3.0 g, 0.029 mol) and water (20 cm³) in DME (100 cm³) washeated under reflux for 24 h. More 4-(methoxyphenyl)boronic acid (1.0 g,6.5×10⁻³ mol) was added to the cooled reaction mixture, which was thenheated under reflux for a further 24 h. DMF (20 cm³) was added and thesolution heated at 110° C. for 24 h, cooled and dilute hydrochloric acid(100 cm³, 20%) added. The cooled reaction mixture was extracted withdiethyl ether (230 cm³) and the combined ethereal extracts washed withwater (100 cm³), dried (MgSO₄), and concentrated onto silica gel to bepurified by column chromatography [silica gel, DCM:hexane 1:1] andrecrystallisation from an ethanol-DCM mixture to yield a greencrystalline solid (1.86 g, yield 63%), Cr—N, 235° C.; N—I, 265° C.

¹H NMR (CD₂Cl₂) δ: 7.71 (2H, dd), 7.61 (8H, m), 7.37 (2H, d), 7.24 (2H,d), 6.95 (4H, d), 3.84 (6H, s), 2.06 (4H, m), 0.71 (10H, m). IR (KBrpellet cm⁻¹): 2961 (w), 1610 (m), 1561 (m), 1511 (s), 1474 (s), 1441(m), 1281 (m), 1242 (s), 1170 (s), 1103 (m), 829 (m), 790 (s). MS (m/z):584 (M⁺−C₃H₇), 569, 555, 539, 525, 511, 468, 313, 277 (M100), 248, 234.Elemental analysis. Calculated: wt % C=78.56%; H, 6.11%; S, 10.23%.Found: C, 78.64%; H, 6.14%; S, 10.25%.

2,7-bis[5-(4-Hydroxyphenyl)thien-2-yl]-9,9-dipropylfluorene): A 1Msolution of boron tribromide in chloroform (9 cm³, 9.0 mmol) was addeddropwise to a stirred solution of2,7-bis[5-(4-methoxyphenyl)thien-2-yl]-9,9-dipropylfluorene (1.3 g,2.1×10⁻³ mol) at 0° C. The temperature was allowed to rise to RTovernight and the solution added to ice-water (200 cm³) with vigorousstirring. The product was extracted into diethyl ether (220 cm³), washedwith aqueous sodium carbonate (2M, 150 cm³), dried (MgSO₄) and purifiedby column chromatography [silica gel DCM:diethyl ether:ethanol 40:4:1]to yield a green solid (1.2 g, yield 96%), Cr—I, 277° C.; N—I, 259° C.

¹H NMR (d-acetone) δ: 8.56 (2H, s), 7.83 (2H, dd), 7.79 (2H, d), 7.68(2H, dd), 7.57 (4H, dd), 7.50 (2H, dd), 7.31 (2H, dd), 6.91 (4H, dd),2.15 (4H, m), 0.69 (10H, m). IR (KBr pellet cm⁻¹): 3443 (s, broad), 2961(m), 1610 (m), 1512 (m), 1474 (m), 1243 (m), 1174 (m), 1110 (w), 831(m), 799 (s). MS (m/z): 598 (M⁺), 526, 419 (M100), 337.

Compound 3:2,7-bis(5-{4-[5-(1-Vinyl-allyloxycarbonyl)pentyloxy]phenyl}thien-2-yl)-9.9-dipropylfluorene:The 1,3-pentadiene monomer (Compound 3) was synthesised as depicted inReaction Scheme 2. Full details of each step are now given:

1,4-Pentadien-3-yl 6-bromohexanoate: A solution of 6-bromohexanoylchloride (3.2 g, 0.026 mol) in DCM (30 cm³) was added dropwise to asolution of 1,4-pentadien-3-ol (2.0 g, 0.024 mol) and triethylamine (2.4g, 0.024 mol) in DCM (30 cm³). The mixture was stirred for 1 h andwashed with dilute hydrochloric acid (20%, 50 cm³), saturated potassiumcarbonate solution (50 cm³), water (50 cm³) then dried (MgSO₄) andconcentrated to a brown oil. The product was purified by dry flashchromatography [silica gel, DCM] to yield a pale yellow oil (4.7 g,yield 75%). Purity >95% (GC).

¹H NMR (CDCl₃) δ: 5.82 (2H, m), 5.72 (1H, m), 5.30 (2H, d), 5.27 (2H,d), 3.42 (2H, t), 2.37 (2H, t), 1.93 (2H, m), 1.72 (2H, m), 1.54 (2H,m). IR (KBr pellet cm⁻¹): 3095 (w), 1744 (s), 1418 (w), 1371 (w), 12521(m), 1185 s), 983 (m), 934 (m). MS (m/z): 261 (M⁺), 177, 67.

2,7-bis(5-{4-[5-(1-Vinyl-allyloxycarbonyl)pentyloxy]phenyl}thien-2-yl)-9,9-dipropylfluorene:A mixture of 2,7-bis[5-(4-hydroxyphenyl)thien-2-yl]-9,9-dipropylfluorene(0.6 g, 1.0×10⁻³ mol), 1,4-pentadien-3-yl 5-bromohexanoate (0.7 g,2.7×10⁻³ mol) and potassium carbonate (0.5 g, 3.6×10⁻³ mol) inacetonitrile (25 cm³) was heated at 50° C. for 18 h. The mixture wasthen heated under reflux conditions for a further 20 h. Excess potassiumcarbonate was filtered off and precipitated product rinsed through withDCM (230 cm³). The solution was concentrated onto silica gel forpurification by column chromatography [silica gel, DCM:hexane 1:1gradients to DCM] and recrystallisation from a DCM-ethanol mixture toyield a green-yellow solid (0.4 g, yield 40%), Cr—N, 92° C.; N—I, 108°C.

¹H NMR (CD₂Cl₂) δ: 7.69 (2H, d), 7.58 (8H, m), 7.35 (2H, d), 7.22 (2H,d), 6.91 (4H, d), 5.83 (4H, m), 5.68 (2H, m), 5.29 (2H, t), 5.25 (2H,t), 5.21 (2H, t), 5.19 (2H, t), 3.99 (4H, t), 2.37 (4H, t), 2.04 (4H,m), 1.80 (4H, quint), 1.70 (4H, quint), 1.51 (4H, quint) 0.69 (10H, m).IR (KBr pellet cm⁻¹): 2936 (m), 2873 (m), 1738 (s), 1608 (m), 1511 (m),1473 (s), 1282 (m), 1249 (s), 1177 (s), 1110 (m), 982 (m), 928 (m), 829(m), 798 (s). APCI-MS (m/z): 958 (M⁺), 892 (M100). Elemental analysis.Calculated: wt % C=76.37; wt % H=6.93; wt % S=6.68. Found: wt % C=75.93;wt % H=6.95; wt % S=6.69.

Compound 4:2,7-bis(5-{4-[5-(1-Allylbut-3-enyloxycarbonyl)pentyloxy]phenyl}thien-2-yl)-9,9-dipropylfluorene:

The 1,3-heptadiene monomer (Compound 4) was synthesised as depicted inreaction Scheme 3. Full details of each step are now given:

1,6-Heptadien-5-yl 5-bromopentanoate: 5-Bromopentanoyl chloride (3.0 g,0.015 mol) was added dropwise to 1,6-heptadien-4-ol (1.5 g, 0.013 mol)and triethylamine (1.4 g, 0.014 mol) in DCM (25 cm³). The mixture wasstirred for 2 h and washed with dilute hydrochloric acid (20%, 50 cm³),saturated aqueous potassium carbonate solution (50 cm³), water (50 cm³)then dried (MgSO₄) and concentrated to a brown oil. The product waspurified by dry flash chromatography [silica gel, DCM] to yield a paleyellow oil (1.7 g, yield 48%). Purity >92% (GC).

¹H NMR (CDCl₃) δ: 5.74 (2H, m), 5.08 (4H, m), 4.99 (1H, m), 3.41 (2H,t), 2.31 (6H, m), 1.88 (2H, m), 1.76 (2H, m). IR (Film cm⁻¹): 2952 (m),1882 (w), 1734 (s), 1654 (m) 1563 (w), 1438 (m), 1255 (m), 1196 (s), 996(m), 920 (s). MS (m/z): 275 (M⁺), 245, 219, 191, 183, 163 (M100), 135,95, 79.

2,7-bis(5-{4-[5-(1-Allylbut-3-enyloxycarbonyl)pentyloxy]phenyl}thien-2-yl)-9,9-dipropylfluorene:A mixture of 2,7-bis[5-(4-hydroxyphenyl)thien-2-yl]-9,9-dipropylfluorene(0.3 g, 1.0×10⁻³ mol), 1,6-heptadienyl 6-bromohexanoate (0.7 g, 2.7×10⁻³mol) and potassium carbonate (0.5 g, 3.6×10⁻³ mol) in acetonitrile (25cm³) was heated under reflux for 20 h. Excess potassium carbonate wasfiltered off and precipitated product rinsed through with DCM (230 cm³).The solution was concentrated onto silica gel for purification by columnchromatography [silica gel, DCM: hexane 1:1 gradients to DCM] andrecrystallisation from a DCM-ethanol mixture to yield a green-yellowsolid (0.21 g, yield 21%), Cr—I, 97° C., N—I, 94° C.

¹H NMR (CDCl₃) δ: 7.68 (2H, d), 7.60 (2H, dd), 7.58 (2H, d), 7.57 (2H,d), 7.33 (2H, d), 7.20 (2H, d), 6.91 (2H, d), 5.75 (4H, m), 5.08 (8H,m), 5.00 (2H, quint), 4.00 (4H, t), 2.33 (12H, m), 2.02 (4H, t), 1.82(4H, quint), 1.71 (4H, quint), 1.53 (4H, m), 0.72 (10H, m). IR (KBrpellet cm⁻¹): 3443 (s), 2955 (s), 1734 (s), 1643 (w), 1609 (m), 1512(m), 1473 (s), 1249 (s), 1178 (s), 996 (m), 918 (m), 829 (m), 799 (s).APCI-MS (m/z): 1015 (M⁺, M100), 921. Elemental analysis. Calculated: wt% C=76.89; wt % H=7.35; wt % S=6.32%. Found: wt % C=76.96; wt % H=7.42;wt % S=6.23.

Compound 5:2,7-bis(5-{4-[3-(1-Vinylallyloxycarbonyl)propyloxy]phenyl}thien-2-yl)-9,9-dipropylfluorene

The 1,3-pentadiene homologue (Compound 5) was synthesised as depicted inreaction Scheme 4. Full details of each step are now given:

4-Bromobutanoyl chloride: Oxalyl chloride (15.2 g, 0.12 mol) was addeddropwise to a stirred solution of 4-bromobutanoic acid (10.0 g, 0.060mol) and DMF (few drops) in chloroform (30 cm³). The solution wasstirred overnight under anhydrous conditions and concentrated to a palebrown oil which was filtered to remove solid impurities (11.0 g, yield99%).

1,4-Pentadien-3-yl 4-bromobutanoate: 4-Bromobutanoyl chloride (3.0 g,0.016 mol) was added dropwise to a solution of 1,4-pentadien-3-ol (1.3g, 0.015 mol) and triethylamine (1.5 g, 0.015 mol) in DCM (30 cm³). Thesolution was stirred for 2 h and washed with dilute hydrochloric acid(20%, 50 cm³), saturated potassium carbonate solution (50 cm³), water(50 cm³) then dried (MgSO₄) and concentrated to a pale brown oil. Theproduct was purified by dry flash chromatography [silica gel, DCM] toyield a pale yellow oil (1.8 g, yield 51%). Purity >85% (GC;decomposition on column).

¹H NMR (CDCl₃) δ: 5.83 (2H, m), 5.72 (1H, m), 5.27 (4H, m), 3.47 (2H,t), 2.55 (2H, t), 2.19 (2H, quint). IR (KBr pellet cm⁻¹): 3096 (w), 2973(w), 1740 (s), 1647 (w), 1419 (m), 1376 (m), 1198 (s), 1131 (s), 987(s), 932 (s), 557 (w). MS (m/z): 217, 166, 152, 149, 125, 110, 84, 67(M100).

2,7-bis(5-{4-[3-(1-Vinylallyloxycarbonyl)propyloxy]phenyl}thien-2-yl)-9,9-dipropylfluorene:A mixture of 2,7-bis[5-(4-hydroxyphenyl)thien-2-yl]-9,9-dipropylfluorene(0.25 g, 4.2×10⁻⁴ mol), 1,4-pentadien-3-yl 4-bromobutanoate (0.40 g,1.7×10⁻³ mol) and potassium carbonate (0.20 g, 1.4×10⁻³ mol) in DMF (10cm³) was heated under reflux for 4 h. The cooled solution was filtered,rinsed through with DCM (3×20 cm³) and concentrated to a pale green oilwhich was purified by column chromatography [silica gel, DCM:hexane 2:1]followed by recrystallisation from ethanol:DCM to yield a green-yellowpowder (0.20 g, yield 53%), Cr—N, 92° C.; N—I, 116° C.

¹H NMR (CDCl₃) δ: 7.61 (10H, m), 7.33 (2H, d), 7.20 (2H, d), 6.92 (4H,d), 5.85 (4H, m), 5.74 (2H, m), 5.32 (4H, d, J=17 Hz), 5.24 (4H, d, J=10Hz), 4.06 (4H, t), 2.56 (4H, t), 2.16 (4H, quint), 2.05 (4H, t), 0.72(10H, m). IR (KBr pellet cm⁻¹): 3449 (m), 2960 (m), 1738 (s), 1609 (m),1512 (m), 1473 (s), 1380 (w), 1249 (s), 1174 (s), 1051 (m), 936 (m), 830(m), 799 (s). APCI-MS (m/z): 903 (M⁺), 837 (M100), 772. Elementalanalysis. Calculated: wt % C=75.80; wt % H=6.47; wt % S=7.10. Found: wt% C=76.13; wt % H=6.48%; wt % S=6.91.

Compound 6:2,7-bis{5-[4-(8-Diallylaminooctyloxy)phenyl]-thien-2-yl}-9,9-dipropylfluorene

The method of preparation of the N,N-diallylamine monomer (Compound 6)is shown in reaction Scheme 5. Full details of each step are now given:

8-Diallylaminooctan-1-ol. A mixture of 8-bromooctan-1-ol (10.0 g, 0.048mol), diallylamine (4.85 g, 0.050 mol) and potassium carbonate (7.0 g,0.051 mol) in butanone (100 cm³) was heated under reflux for 18 h.Excess potassium carbonate was filtered off and the solutionconcentrated to a colourless oil. The product was purified by dry flashchromatography [silica gel, DCM:ethanol 4:1]. (10.0 g, yield 93%)

¹H NMR (CDCl₃) δ: 5.86 (2H, d), 5.14 (4H, m), 3.71 (4H, quart), 3.63(4H, t), 3.09 (4H, d), 1.56 (4H, m), 1.45 (2H, quint), 1.30 (6H,m). IR(KBr pellet cm⁻¹): 3344 (s), 2936 (s), 1453 (w), 1054 (m), 998 (m), 921(m). MS (m/z): 225 (M⁺), 198, 184, 166, 152, 138, 124, 110 (M100), 81.

Toluene-4-sulphonic acid 8-diallylaminooctyl ester. 4-Toluene-sulphonylchloride (12.5 g, 0.066 mol) was added slowly to a stirred solution of8-diallylaminooctan-1-ol (10.0 g, 0.044 mol) and pyridine (7.0 g, 0.088mol) in chloroform (100 cm³) at 0° C. After 24 h, water (100 cm³) wasadded and the solution washed with dilute hydrochloric acid (20%, 100cm³), sodium carbonate solution (100 cm³), water (100 cm³), dried(MgSO₄) and concentrated to a yellow oil which was purified by columnchromatography [silica gel, 4% diethyl ether in hexane eluting toDCM:ethanol 10:1] to yield the desired product (6.7 g, yield 40%).

¹H NMR (CDCl₃) δ: 7.78 (2H, d), 7.34 (2H, d), 5.84 (2H, m), 5.13 (4H,m), 4.01 (2H, t), 3.41 (4H, d), 2.45 (3H, s), 2.39 (2H, t), 1.63 (2H,quint), 1.42 (2H, quint), 1.30 (2H, quint), 1.23 (6H, m). IR (KBr pelletcm⁻¹): 3454 (w), 2957 (m), 1453 (s), 1402 (m), 1287 (m), 1159 (w), 1061(m), 914 (w), 878 (m), 808 (s), 448 (m). MS (m/z): 380 (M⁺), 364, 352,338, 224, 110 (M1100), 91, 79, 66.

2,7-bis{5-[4-(8-Diallylaminooctyloxy)phenyl]-thien-2-yl}-9,9-dipropylfluorene:A mixture of 2,7-bis[5-(4-hydroxyphenyl)thien-2-yl]-9,9-dipropylfluorene(0.5 g, 8.4×10⁻⁴ mol), toluene-4-sulphonic acid-8-diallylaminooctylester (0.8 g, 2.1×10⁻³ mol) and potassium carbonate (0.3 g, 2.2×10⁻³mol) in butanone (30 cm³) was heated under reflux for 24 h. Excesspotassium carbonate was filtered off and rinsed with DCM (3×30 cm³). Thesolution was concentrated onto silica gel for purification by columnchromatography [silica gel, DCM:hexane 2:1 eluting to DCM:ethanol 4:1].The product was obtained as a yellow-green glass (0.35 g, yield 41%),N—I, 95° C.

¹H NMR (CDCl₃) δ: 7.67 (2H, d), 7.58 (8H, m), 7.34 (2H, d), 7.20 (2H,d), 6.92 (4H, d), 5.94 (4H, m), 5.25 (8H, m), 3.99 (4H, t), 3.22 (8H,d), 2.02 (4H, t), 1.80 (4H, quint), 1.56 (4H, quint), 1.47 (4H, quint),1.35 (12H, m), 0.71 (10H, m). IR (KBr pellet cm⁻¹): 3437 (s), (2934 (s),1609 (s), 1512 (s), 1472 (s), 1283 (m), 1249 (s), 1179 (s), 1031 (w),918 (w), 829 (m), 798 (s). APCI-MS (m/z): 1014 (M⁺, M100), 973.Elemental analysis. Calculated: wt % C=79.40; wt % H=8.35; wt % N=2.76;wt % S=6.33. Found: wt % C=79.33; wt % H=8.29; wt % N=2.88; wt % S=6.17.

Compound 7:poly(phenylene-1,3,4-oxadiazole-phenylene-hexafluoropropylene)

The electron-transporting polymer (Compound 7) was prepared according toa literature method described in Li, X.-C.; Kraft, A.; Cervini, R.;Spencer, G. C. W.; Cacialli, F.; Friend, R. H.; Gruener, J.; Holmes, A.B.; de Mello, J. C.; Moratti, S. C. Mat. Res. Symp. Proc. 1996, 413 13.

In more detail the preparation details were as follows: A solution of4,4′-(hexafluoroisopropylidine)bis(benzoic acid) (2.54 g, 6.48×10⁻³ mol)and hydrazine sulphate (0.84 g, 6.48×10⁻³ mol) in Eaton's reagent (25cm³) was heated under reflux for 18 h. The cooled solution was added tobrine (300 cm³) and the product extracted into chloroform (8×200 cm³).The organic extracts were combined, dried (MgSO₄) and the solventremoved under reduced pressure to yield the crude product which waspurified by dissolving in a minimum volume of chloroform andprecipitating by dropwise addition to methanol (1000 cm³). Theprecipitate was filtered off and washed with hot water before beingdried in vacuo. The precipitation was repeated a further three timeswashing with methanol each time. The product was then dissolved inchloroform and passed through a microfilter (0.45 μm). The pure productwas then precipitated in methanol (500 cm³) and the methanol removedunder reduced pressure to yield a white fibrous solid which was dried invacuo. Yield 1.26 g (50%).

¹H NMR (CDCl₃) δ_(H):8.19 (4H/repeat unit, d), 7.61 (4H/repeat unit, d).IR ν_(max)/cm⁻¹: 3488 (m), 1621 (m), 1553 (m), 1502 (s), 1421 (m), 1329(m), 1255 (s), 1211 (s), 1176 (s), 1140 (s), 1073 (m), 1020 (m), 969(m), 929 (m), 840 (m), 751 (m), 723 (s). GPC: M_(w):M_(n)=258211:101054.

An alternative electron-transport copolymer is prepared according to themethod described in Xiao-Chang Li et al J. Chem. Soc. Chem. Commun.,1995, 2211.

In more detail the preparation details were as follows: Terephthaloylchloride (0.50 g, 2.46×10⁻³ mol) was added to hydrazine hydrate (50 cm³)at room temperature and the mixture stirred for 2 h. The precipitate wasfiltered off, washed with water (100 cm³) and dried in vacuo. The crudehydrazide (0.25 g, 1.3×10⁻³ mol),4,4′-(hexafluoroisopropylidine)bis(benzoic acid) (2.50 g, 6.4×10⁻³ mol)and hydrazine sulphate (0.66 g, 5.2×10⁻³ mol) were added to Eaton'sreagent and the resultant mixture heated at 100° C. for 24 h. Thereaction mixture was added to water (300 cm³) and the product extractedinto chloroform (3×300 cm³). The organic extracts were combined, dried(MgSO₄) and the solvent removed in vacuo before re-dissolving theproduct in the minimum volume of chloroform. The solution was addeddropwise to methanol (900 cm³) to give a white precipitate which wasfiltered off and dried in vacuo. The precipitation was repeated twicebefore dissolving the product in chloroform and passing through amicrofilter (0.45 μm) into methanol (500 cm³). The methanol was removedunder reduced pressure and the product dried in vacuo. Yield 1.1 g (41%)

¹H NMR (CDCl₃) δ_(H):8.18 (dd, 4H/repeat unit), 7.60 (dd, 4H/repeatunit). IR ν_(max)/cm⁻¹: 3411 (w), 2366 (w), 1501 (m), 1261 (s), 1211(s), 1176 (s), 1140 (m), 1072 (m), 1021 (w), 968 (m), 931 (w), 840 (m),722 (m). GPC: M_(w):M_(n)=20572:8320.

Key intermediate 2: 9,9-diethyl-2,7-bis(4-hydroxybiphenyl-4′-yl)fluorenewas synthesised as shown in Reaction Scheme 7. Full details of each stepare now given:

9-Ethylfluorene: A solution of n-butyllithium (79.52 cm³, 0.2168 mol,2.5M in hexane) was added slowly to a solution of fluorene (30.00 g,0.1807 mol) in THF (300 cm³) at −70° C. The solution was stirred for 1hour at −75° C. and 1-bromoethane (17.59 cm³, 0.2349 mol) was addedslowly. The solution was allowed to warm to room temperature and thenstirred overnight. Dilute hydrochloric acid (200 ml, 20%) was added tothe reaction mixture and stirred for a further 10 minutes. Water (250cm³) was added and the product extracted into diethyl ether (3×300 cm³).The combined organic extracts were dried (MgSO₄) and the solvent removedon a rotary evaporator. The resulting oil was purified by distillationto yield a pale yellow oil (25.00 g, 71%, b.pt. −150° C. @ 1 mbar Hg).

¹H NMR (DMSO) δ: 7.70 (2H, m), 7.50 (2H, m), 7.30 (4H, m), 4.00 (1H, t),2.02 (2H, quart), 0.31 (3H, t). IR ν_(max)/cm⁻¹: 3072 (m), 2971, 1618,1453, 1380, 1187, 759, 734. MS m/z: 170 (M⁺), 94, 82, 69.

9,9-Diethylfluorene: A solution of n-butyllithium (77.34 cm³, 0.1934mol, 2.5M in hexane) was added slowly to a solution of 9-ethylfluorene(25.00 g, 0.1289 mol) in THF (250 cm³) at −70° C. The solution wasstirred for 1 hour at −75° C. and 1-bromoethane (17.59 cm³, 0.1934 mol)was added slowly. The solution was allowed to warm to room temperatureand then stirred overnight. Dilute hydrochloric acid (200 cm³, 20%) wasadded to the reaction mixture and stirred for a further 10 minutes.Water (250 cm³) was added and the product extracted into diethyl ether(3×300 cm³). The combined organic extracts were dried (MgSO₄) and thesolvent removed on a rotary evaporator. The resulting oil was cooled toroom temperature and recrystallised with ethanol to yield white crystals(19.50 g, 68%, m.pt. 60-62° C.).

¹H NMR (DMSO) δ: 7.76 (2H, m), 7.51 (2H, m), 7.35 (4H, m), 1.51 (4H,quart), 0.30 (6H, t), IR ν_(max)/cm⁻¹: 3069, 2972, 1612, 1448, 1310,761, 736. MS m/z: 222 (M⁺), 193, 152, 94, 82, 75.

2,7-Dibromo-9,9-diethylfluorene: Bromine (13.47 cm³, 0.2568 mol) wasadded to a stirred solution of 9,9-diethylfluorene (19.00 g, 0.0856 mol)in DCM (250 cm³). The HBr gas evolved was passed through a scrubbingsolution of NaOH (1.5M). The reaction mixture was stirred for 4 hours.The reaction mixture was washed with sodium metabisulphite solution andextracted into diethyl ether (3×300 cm³). The combined organic extractswere dried and the solvent removed on a rotary evaporator. The crudeproduct was recrystallised from ethanol to yield a white crystallinesolid (20.00 g, 61%, m.pt. 152-154° C.).

¹H NMR (DMSO) δ: 7.52 (2H, m), 7.45 (4H, m), 1.99 (4H, quart), 0.31 (6H,t). IR ν_(max)/cm⁻¹: 2966, 1599, 1453, 1418, 1058, 772, 734. MS m/z: 380(M⁺), 351, 272, 220, 189, 176, 165, 94, 87, 75.

4-Bromo-4′-octyloxybiphenyl: A mixture of 4-bromo-4′-hydroxybiphenyl(50.00 g, 0.2008 mol), 1-bromooctane (50.38 g, 0.2610 mol), potassiumcarbonate (47.11 g, 0.3414 mol) and butanone (500 cm³) was heated underreflux overnight. The cooled mixture was filtered and the solventremoved on a rotary evaporator. The crude solid was recrystallised fromethanol to yield a white crystalline solid (47.30 g, 66%, m.pt. 120°C.).

¹H NMR (DMSO) δ: 7.46 (6H, m), 6.95 (2H, m), 3.99 (2H, t), 1.80 (2H,quint), 1.38 (10H, m), 0.88 (3H, t). IR ν_(max)/cm⁻¹: 2927, 2860, 1608,1481, 1290, 1259, 844. MS m/z: 362 (M⁺), 250, 221, 195, 182, 152, 139,115, 89, 76, 69.

4-Octyloxybiphenyl-4′-yl boronic acid: A solution of n-butylithium(50.97 cm³, 0.1274 mol, 2.5M in hexane) was added dropwise to a cooled(−78° C.) stirred solution of 4-bromo-4′-octyloxybiphenyl (40.00 g,0.1108 mol) in THF (400 cm³). After 1 h, trimethyl borate (23.05 g,0.2216 mol) was added dropwise to the reaction mixture maintaining atemperature of −78° C. The reaction mixture was allowed to warm to roomtemperature overnight. 20% hydrochloric acid (350 cm³) was added and theresultant mixture stirred for 1 h. The product was extracted intodiethyl ether (3×300 cm³). The combined organic layers were washed withwater (300 cm³), dried (MgSO₄), filtered and the filtrate evaporateddown under partially reduced pressure. The crude product was stirredwith hexane for 30 minutes and filtered off to yield a white powder(26.20 g, 73%, m.pt. 134-136° C.).

¹H NMR (DMSO) δ: 8.04 (2H, s), 7.84 (2H, m), 7.57 (4H, m), 7.00 (2H, m),3.99 (2H, t), 1.74 (2H, quint), 1.35 (10H, m), 0.85 (3H, t). IRν_(max)/cm⁻¹: 2933, 2860, 1608, 1473, 1286, 1258, 818. MS m/z: 326 (M⁺),214, 196, 186, 170, 157, 128, 115, 77, 63

9,9-Diethyl-2,7-bis(4-octyloxybiphenyl-4′-yl)fluorene:

Tetrakis(triphenylphosphine)palladium(0) (0.70 g, 0.0006 mol) was addedto a stirred solution of 2,7-dibromo-9,9-diethylfluorene (4) (2.33 g,0.0061 mol), 4-octyloxybiphenyl-4′-yl boronic acid (5.00 g, 0.0153 mol),20% sodium carbonate solution (100 cm³) and 1,2-dimethoxyethane (150cm³). The reaction mixture was heated under reflux overnight. Water (300cm³) was added to the cooled reaction mixture and the product extractedinto DCM (3×300 cm³). The combined organic extracts were washed withbrine (2×150 cm³), dried (MgSO₄₎), filtered and the filtrate evaporateddown under partially reduced pressure. The residue was purified bycolumn chromatography on silica gel using DCM and hexane (30:70) aseluent and recrystallisation from ethanol and DCM to yield a whitecrystalline solid (3.10 g, 65%, m.pt. 146° C.).

¹H NMR (DMSO) δ: 7.77 (6H, m), 7.63 (12H, m), 7.00 (4H, m), 4.01 (4H,t), 2.13 (4H, quart), 1.82 (4H, quint), 1.40 (20H, m), 0.89 (6H, t),0.43 (6H, t). IR ν_(max)/cm⁻¹: 3024, 2921, 2853, 1609, 1501, 1463, 1251,808. MS m/z: 782 (M⁺), 669, 514, 485, 279, 145, 121, 107, 83, 71. CHNanalysis: % Expected C, (87.42%); H, (8.49%). % Found C, (87.66%); H,(8.56%).

9,9-Diethyl-2,7-bis(4-hydroxybiphenyl-4′-yl)fluorene: Boron tribromide(99.9%, 1.05 cm³, 0.0111 mol) in DCM (10 ml) was added dropwise to acooled (0° C.) stirred solution of9,9-diethyl-2,7-bis(4-octyloxybiphenyl-4′-yl)fluorene (2.90 g, 0.0037mol) in DCM (100 cm³). The reaction mixture was stirred at roomtemperature overnight, then poured onto an ice/water mixture (50 g) andstirred (30 minutes). The crude product was purified by columnchromatography on silica gel with a mixture of ethyl acetate and hexane(30:70) as the eluent and recrystallisation from ethanol to yield awhite powder (0.83 g, 40%, m.pt. >300° C.).

¹H NMR (DMSO) δ: 9.09 (2H, OH), 7.77 (6H, m), 7.64 (8H, m), 7.51 (4H,m), 6:94 (4H, m), 1.19 (4H, m), 0.42 (6H, t). IR ν_(max)/cm⁻¹: 1608,1500, 1463, 1244, 1173, 811. MS m/z: 558 (M⁺), 529, 514, 313, 279, 257,115, 77, 65.

Compound 8:9,9-Diethyl-2,7-bis{4-[5-(1-vinyl-allyloxycarbonyl)pentyloxy]biphenyl-4′-yl}fluorene:Compound 8 was synthesised as follows:

A mixture of 9,9-diethyl-2,7-bis(4-hydroxybiphenyl-4′-yl)fluorene (0.83g, 0.0015 mol), 1,4-pentadienyl-3-yl 6-bromohexanoate (0.97 g, 0.0037mol), potassium carbonate (0.62 g, 0.0045 mol) and DMF (25 cm³) washeated under reflux overnight. The cooled reaction mixture was added towater (500 cm³) and then extracted with DCM (3×50 cm³). The combinedorganic extracts were washed with water (250 cm³), dried (MgSO₄) and thefiltrate evaporated down under partially reduced pressure. The crudeproduct was purified by column chromatography using silica gel using amixture of DCM and hexane (80:20) as the eluent and recrystallisationfrom DCM and ethanol to yield a white crystalline solid (0.2 g, 22%).

¹H NMR (CDCl₃) δ: 7.78 (6H, m), 7.62 (12H, m), 7.00 (4H, m), 5.85 (4H,m), 5.74 (4H, m), 5.27 (4H, m), 4.03 (4H, t), 2.42 (4H, t), 2.14 (4H,quart), 1.85 (4H, m), 1.74 (4H, m), 1.25 (4H, q), 0.43 (3H, t). IRν_(max)/cm⁻¹: 3028, 2922, 2870, 1734, 1606, 1500, 1464, 1246, 1176, 812.CHN analysis: % Expected C, (82.32%); H, (7.24%). % Found C, (81.59%);H, (6.93%).

Compounds 9-15: Compounds 9 to 15, comprising the2,7-bis{ω-[5-(1-vinyl-allyloxycarbonyl)alkoxy]-4′-biphenyl}9,9-dialkylfluorenescompounds of Table 1 were prepared analogously to Compound 8.

n m Compound 9 3  5 Compound 10 4  5 Compound 11 5  5 Compound 12 6  5Compound 13 8  5 Compound 14 8  7 Compound 15 8 11Compound 16:4,7-bis{4-[(S)-3,7-Dimethyl-oct-6-enyloxy]phenyl}-2,1,3-benzothiadozole

Compound 16 was synthesised as depicted in Reacton Scheme 8. Fulldetails of each step follows:

4,7-Dibromo-2,1,3-benzothiadozole: Bromine (52.8 g, 0.33 mol) was addedto a solution of 2,1,3-benzothiadozole (8.1 g, 0.032 mol) in hydrobromicacid (47%, 100 cm³) and the resultant solution was heated under refluxfor 2.5 h. The cooled reaction mixture reaction mixture was filtered andthe solid product washed with water (200 cm³) and sucked dry. The rawproduct was purified by recrystallisation from ethanol to yield 21.0 g(65%) of the desired product.

1-Bromo-4-[(S)-3,7-dimethyloct-6-enyloxy]benzene: A mixture of4-bromophenol (34.6 g, 0.20 mol), (S)-(+)-citronellyl bromide (50g,0.023 mol) and potassium carbonate (45 g, 0.33 mol) in butanone (500cm³) was heated under reflux overnight. The cooled reaction mixture wasfiltered and the filtrate concentrated under reduced pressure. The crudeproduct was purified by fractional distillation to yield 42.3 g (68.2%)of the desired product.

4-[(S)-3,7-Dimethyloct-6-enyloxy]phenyl boronic acid: 2.5M n-Butylithiumin hexanes (49.3 cm³, 0.12 mol) was added dropwise to a cooled (−78° C.)solution of 1-bromo-4-[(S)-3,7-dimethyloct-6-enyloxy]benzene (35 g, 0.11mol) in tetrahydrofuran (350 cm³). The resultant solution was stirred atthis temperature for 1 h and then trimethyl borate (23.8 g, 0.23 mol)was added dropwise to the mixture while maintaining the temperature at−78° C. 20% hydrochloric acid (250 cm³) was added and the resultantmixture was stirred for 1 h and then extracted into diethyl ether (2×200cm³). The combined organic layers were washed with water (2×100 cm³) anddried (MgSO₄). After filtration the solvent was removed under reducepressure to yield 20.35 g (65%) of the desired product.

4,7-bis{4-[(S)-3,7-Dimethyl-oct-6-enyloxy]phenyl}-2,1,3-benzothiadozole:A mixture of tetrakis(triphenylphosphine)palladium(0) (0.8 g, 0.70×10⁻³mol), 4,7-dibromo-2,1,3-benzothiadozole (2) (2 g, 6.75×10⁻³ mol),4-[(S)-3,7-dimethyloct-6-enyloxy]phenyl boronic acid (4.66 g, 1.70×10⁻²mol), 2M sodium carbonate solution (50 cm³) and 1,2-dimethoxyethane (150cm³). The reaction mixture was heated under reflux overnight. The cooledreaction mixture was extracted with dichloromethane (2×150 cm³) and thecombined organic layers were washed with brine (2×100 cm³) and dried(MgSO₄). After filtration the solvent was removed under reduced pressureand the residue was purified by column chromatography [silica gel,dichloromethane: hexane 1:4] followed by recrystallisation from ethanolto yield 3.2 g (79.5%) of the desired product.

4,7-bis(4-Hydroxyphenyl)-2,1,3-benzothiadozole: Boron tribromide (1.51cm³, 1.61×10⁻² mol) was added dropwise to a cooled (0° C.) stirredsolution of2,5-bis{4-[(S)-3,7-dimethyl-oct-6-enyloxy]phenyl}-2,1,3-benzothiadozole(4.0 g, 7.40×10⁻³ mol) in dichloromethane (100 cm³). The reactionmixture was stirred at room temperature overnight, then poured onto anice/water mixture (200 g) and stirred (30 min). The desired product wasprecipitated and it was filtered off and sucked dry to yield 1.23 g(71.5%) of the desired product.

4,7-bis(4-{5-[1-Vinyl-allyloxycarbonyl]pentyloxy}phenyl)-2,1,3-benzothiadozole:A mixture of 2,5-bis(4-hydroxyphenyl)-2,1,3-benzothiadozole (0.3 g,0.93×10⁻³ mol), 1,4-pentadien-3-yl 5-bromopentanoate (0.61 g, 2.34×10⁻³mol) and potassium carbonate (0.38 g, 2.79×10⁻³ mol) inN,N-dimethylformaldehyde (30 cm³) was heated (80° C.) overnight. Thecooled reaction mixture was filtered and the filtrate concentrated underreduce pressure. The crude product was purified by column chromatography[silica gel, ethyl acetate: hexane 1:5] followed by recrystallisationfrom ethanol to yield 0.39 g (61.8%) of the desired product.

Compounds 17 and 18 are preparable by an analogous process.

Thin Film Polymerisation and Evaluation

Thin films of Compounds 3 to 6 and Compounds 9 to 15 were prepared byspin casting from a 0.5%-2% M solution in chloroform onto quartzsubstrates. All sample processing was carried out in a dry nitrogenfilled glove box to avoid oxygen and water contamination. The sampleswere subsequently baked at 50° C. for 30 minutes, heated to 90° C. andthen cooled at a rate of 0.2° C. to room temperature to form a nematicglass. Polarised microscopy showed that no change was observed in thefilms over several months at room temperature. The films werepolymerized in a nitrogen filled chamber using light from an Argon Ionlaser. Most of the polymerization studies were carried out at 300 nmwith a constant intensity of 100 MWcm⁻² and the total fluence variedaccording to the exposure time. No photoinitiator was used. Temperaturedependent polymerization studies were carried out in a Linkham model LTS350 hot-stage driven by a TP 93 controller under flowing nitrogen gas. Asolubility test was used to find the optimum fluence: different regionsof the film were exposed to UV irradiation with different fluences andthe film was subsequently washed in chloroform for 30 s. Theunpolymerized and partially polymerized regions of the film were washedaway and PL from the remaining regions was observed on excitation withan expanded beam from the Argon Ion laser. Optical absorbancemeasurements were made using a Unicam 5625 UV-VIS spectrophotometer. PLand EL were measured in a chamber filled with dry nitrogen gas using aphotodiode array (Ocean Optics S2000) with a spectral range from 200 nmto 850 nm and a resolution of 2 nm. Films were deposited onto CaF₂substrates for Fourier Transform infra-red measurements, which werecarried out on a Perkin Elmer Paragon 1000 Spectrometer. Indium tinoxide (ITO) coated glass substrates, (Merck 15Ω/) were used for ELdevices. These were cleaned using an Argon plasma. ²⁰A PDOT (EL-grade,Bayer) layer of thickness 45 nm±10% was spin-cast onto the substrate andbaked at 165° C. for 30 minutes. This formed a hole-transporting film.One or more organic films of thickness ≈45 nm were subsequentlydeposited by spin-casting and crosslinked as discussed below. Filmthicknesses were measured using a Dektak surface profiler. Aluminum wasselectively evaporated onto the films at a pressure less than 1×10⁻⁵torr using a shadow mask to form the cathode.

Photopolymerisation Details

The optimum fluences required in order to polymerize the diene monomers(Compounds 3 to 6) efficiently with a minimum of photodegradation, werefound to be 100 Jcm⁻², 20 Jcm⁻², 100 Jcm⁻² and 300 Jcm⁻² respectively,using the solubility test. As Scheme 6 shows, the 1,6-heptadiene monomer(e.g. Compound 4) forms a network with a repeat unit containing a singlering. Its polymerization rate is equal to that of the 1,4-pentadienemonomer (e.g. Compounds 3 and 5) but the increase of PL intensity afterpolymerization is less for Compound 4. This may be because of theincreased flexibility of the C₇ ring in the backbone of the crosslinkedmaterial. The 1,4-pentadiene diene monomers (Compounds 3 and 5) arehomologues and differ only in the length of the flexible alkoxy-spacerpart of the end-groups. The PL spectrum of Compound 5 with the shorterspacer is significantly different to all other materials before exposuresuggesting a different conformation. The higher fluence required topolymerize the 1,4-pentadiene monomer Compound 5 implies that thepolymerization rate is dependent on the spacer length: the freedom ofmotion of the photopolymerizable end-group is reduced, because of theshorter aliphatic spacer in Compound 5. The diallylamine monomerCompound 6 has a significantly different structure to the dienes. It ismuch more photosensitive than the other diene monomers because of theactivation by the electron rich nitrogen atom. Scheme 6 also shows (byway of comparison) that when a methacrylate monomer is employed thepolymerization step does not involve the formation of a ring.

Photopolymerization Characteristics

The absorbance and PL spectra of 1,4-pentadiene monomer (Compound 3)were measured before and after exposure with the optimum UV fluence of100 J cm⁻². The latter measurements were repeated after washing inchloroform for 30 s. The absorbance spectra of the unexposed and exposedfilms are almost identical and the total absorbance decreases by 15%after washing indicating that only a small amount of the material isremoved. This confirms conclusively that a predominantly insolublenetwork is formed.

The UV irradiation was carried out in the nematic glass phases at roomtemperature at 300 nm. The excitation of the fluorene chromophore isminimal at this wavelength and the absorbance is extremely low. Theexperiment was repeated using a wavelength of 350 nm near the absorbancepeak. Although the number of absorbed photons is far greater at 350 nm,a similar fluence is required to form an insoluble network. Furthermoreexcitation at 350 nm results in some photodegradation. UVphotopolymerization was also carried out at 300 nm at temperatures of50° C., 65° C. and 80° C. all in the nematic phase. It was anticipatedthat the polymerization rate would increase, when the photoreactivemesogens were irradiated in the more mobile nematic phase. However, thefluence required to form the crosslinked network was independent oftemperature, within the resolution of our solubility test. Furthermore,the integrated PL intensity from the crosslinked network decreases withtemperature indicating a temperature dependent photodegradation.

Bilayer Electroluminescent Devices

Bilayer electroluminescent devices were prepared by spin-casting the1,4-pentadiene monomer (Compound 3) onto a hole-transporting PEDT layer.The diene functioned as the light-emitting and electron-transportingmaterial in the stable nematic glassy state. Equivalent devices usingcross-linked networks formed from Compound 3 by photopolymerisation withUV were also fabricated on the same substrate under identical conditionsand the EL properties of both types of devices evaluated and compared.The fabrication of such bilayer OLEDs is facilitated by the fact thatthe hole-transporting PEDT layer is insoluble in the organic solventused to deposit the electroluminescent and electron-transportingreactive mesogen (Compound 3). Half of the layer of Compound 3 wasphotopolymerized using optimum conditions and the other half was leftunexposed so that EL devices incorporating either the nematic glass orthe cross-linked polymer network could be directly compared on the samesubstrate under identical conditions. Aluminum cathodes were depositedonto both the cross-linked and non cross-linked regions. Polarizedelectroluminescent devices were prepared by the polymerization ofuniformly aligned Compound 3 achieved by depositing it onto aphotoalignment layer doped with a hole transporting molecule. In thesedevices external quantum efficiencies of 1.4% were obtained forelectroluminescence at 80 cd m⁻². Three layer devices were also preparedby spin-casting an electron transporting polymer (Compound 7), whichshows a broad featureless blue emission, on top of the crosslinkednematic polymer network. In the case of both the three layer and bilayerdevices the luminescence originates from the cross-linked polymernetwork of the 1,4-pentadiene monomer (Compound 3). The increasedbrightness of the three-layer device may result from an improved balanceof electron and hole injection and/or from a shift of the recombinationregion away from the absorbing cathode.

Multilayer Device

A multilayer device configuration was implemented as illustrated in FIG.2. A glass substrate 30 (12 mm×12 mm×1 mm) coated with a layer of indiumtin oxide 32 (ITO) was cleaned via oxygen plasma etching. Scanningelectron microscopy revealed an improvement in the surface smoothness byusing this process which also results in a beneficial lowering of theITO work function. The ITO was coated with two strips (˜2 mm) ofpolyimide 34 along opposite edges of the substrate then covered with apolyethylene dioxthiophene/polystyrene sulfonate (PEDT/PSS) EL-gradelayer 36 of thickness 45±5 nm deposited by spin-coating. The layer 36was baked at 165° C. for 30 min in order to cure the PEDT/PSS and removeany volatile contaminants. The doped polymer blend of Compounds 1 and 2was spun from a 0.5% solution in cyclopentanone forming an alignmentlayer 40 of thickness ˜20 nm. This formed the hole-injecting aligninginterface after exposure to linearly polarized CV from an argon ionlaser tuned to 300 nm. A liquid-crystalline luminescent layer 50 ofCompound 3 was then spun cast from a chloroform solution forming a filmof ˜10 nm thickness. A further bake at 50° C. for 30 min was employed todrive off any residual solvent. The sample was heated to 100° C. andslowly cooled at 02° C./min to room temperature to achieve macroscopicalignment of chromophores in the nematic glass phase. Irradiation withUV light at 300 nm from an argon ion laser was used to inducecrosslinking of the photoactive end-groups of the Compound 3 to form aninsoluble and intractable layer. No photoinitiator was used henceminimizing continued photoreaction during the device lifetime. Aluminiumelectrodes 50 were vapor-deposited under a vacuum of 10° mbar or betterand silver paste dots 52 applied for electrical contact. A silver pastecontact 54 was also applied for contact with the indium tin oxide baseelectrode. This entire fabrication process was carried out under drynitrogen of purity greater than 99.99%. Film thickness was measuredusing a Dektak ST surface profiler.

The samples were mounted for testing within a nitrogen-filled chamberwith spring-loaded probes. The polymide strips form a protective layerpreventing the spring-loaded test probes from pushing through thevarious layers. Optical absorbance measurements were taken using aUnicam UV-vis spectrometer with a polarizer (Ealing Polarcaot 105 UV-viscode 23-2363) in the beam. The spectrometer's polarization bias wastaken into account and dichroic ratios were obtained by comparing maximaat around 370-380 nm.

Luminescence/voltage measurements were taken using a photomultipliertube (EMI 6097B with S11 type photocathode) and Keithley 196 multimeterwith computer control. Polarized EL measurements were taken using aphotodiode array (Ocean Optics S2000, 200-850 nm bandwidth 2 nmresolution) and polarizer as described above. The polarization bias ofthe spectrometer was eliminated by use of an input fiber (fused silica100 μm diameter) ensuring complete depolarisation of light into theinstrument.

Monochrome Backlight

FIG. 3 shows a schematic representation of a polarised light monochromebacklight used to illuminate a twisted nematic liquid crystal display.The arrows indicate the polarisation direction. An inert substrate 30(e.g. glass coated with a layer of indium tin oxide (ITO) as in FIG. 2)is provided with a layer 50 of a polarised light emitting polymer (e.g.comprising Compound 3 as in FIG. 2). The assembly further includes aclean up polariser 60 comprising a high transmission low polarisationefficiency polariser; a twisted nematic liquid crystal display 70; and afront polariser 80. It will be appreciated that the light emittingpolymer layer 50 acts as a light source for the liquid crystal display70.

Polarised Light Sequential Tri-Color Backlight

FIG. 3 schematic of a polarised light sequential red, green and bluelight emitting backlight used to illuminate a fast liquid crystaldisplay (ferroelectric display). The arrows indicate the polarisationdirection. An inert substrate 30 (e.g. glass coated with a layer ofindium tin oxide (ITO) as in FIG. 2) is respectively provided with red52, green 54 and blue 56 striped layers of a polarised light emittingpolymer (e.g. comprising Compound 3 as in FIG. 2 and a suitable dyemolecule as a dopant). The assembly further includes a clean uppolariser 60 comprising a high transmission low polarisation efficiencypolariser; a fast (ferroelectric) liquid crystal display 70; and a frontpolariser 80. It will be appreciated that the striped light emittingpolymer layer 52, 54, 56 acts as a light source for the fast liquidcrystal display 70. The sequential emission of the RGB stripescorresponds with the appropriate colour image on the fast liquid crystaldisplay. Thus, a colour display is seen.

Alignment Characteristics

The PL polarization ratio (PL_(η)/PL_(⊥)) of the aligned polymer formedfrom Compound 3 in its nematic glass phase can be taken as a measure ofthe alignment quality. Optimum alignment is obtained with the undopedalignment layer for an incident fluence of 50 mJ cm⁻². The alignmentquality deteriorates when higher fluences are used. This is expectedbecause there are competing LC-surface interactions giving parallel andperpendicular alignment respectively. When the dopant concentration is40% or higher there is a detrimental effect on alignment. However withconcentrations up to 30% the polarization ratio of emitted light is notseverely effected although higher fluences are required to obtainoptimum alignment. The EL intensity reaches its peak for the ˜50%mixture. A 30% mixture offers a good compromise in balancing the outputluminescence intensity and polarization ratio. From these conditions andusing the 30% doped layer we have observed strong optical dichroism inthe absorbance (D˜6.5) and obtained PL polarization ratios of 8:1.

Electroluminescence Characteristics

Devices made with compound 3 in the nematic glassy state showed poor ELpolarization ratios because the low glass transition temperaturecompromised the alignment stability. Much better performance wasachieved when compound 3 was crosslinked.

A brightness of 60 cd m⁻² (measured without polarizer) was obtained at adrive voltage of 11V. The threshold voltage, EL polarization ratio andintensity all depend on the composition of the alignment layer. Aluminance of 90 cd m⁻² was obtained from a 50% doped device but with areduction in the EL polarization ratio. Conversely a polarized EL ratioof 11:1 is found from a 20% doped device but with lower brightness. Athreshold voltage of 2V is found for the device with a hole-transportinglayer with 100% of the dopant comprising compound 2. Clearly aphoto-alignment polymer optimised for both alignment andhole-transporting properties would improve device performance. Thiscould be achieved using a co-polymer incorporating both linear rod-likehole-transporting and photoactive side chains.

1. A light emitter for a display comprising a photoalignment layer; andaligned on said photoalignment layer, a light emitting polymer.
 2. Alight emitter according to claim 1, wherein the photoalignment layercomprises a chromophore attached to a sidechain polymer backbone by aflexible spacer entity.
 3. A light emitter according to claim 2, whereinthe chromophore is selected from the group consisting of cinnamates,coumarins and any derivatives thereof and any mixtures thereof.
 4. Alight emitter according to claim 3, wherein the chromophore is selectedfrom the group consisting of 6-hydroxycoumarins, 7-hydroxycoumarins andany derivatives thereof and any mixtures thereof.
 5. A light emitteraccording to claim 4, wherein the photoalignment layer comprises the7-hydroxycoumarin compound having the formula:


6. A light emitter according to claim 2, wherein the flexible spacercomprises an unsaturated organic chain.
 7. A light emitter according toclaim 6, wherein the unsaturated organic chain is selected from thegroup consisting of aliphatic, amine and ether linkages.
 8. A lightemitter according to claim 1, wherein the photoalignment layer isphotocurable.
 9. A light emitter according to claim 1, wherein thephotalignment layer is doped with a hole transport compound.
 10. A lightemitter according to claim 9, wherein the hole transport compound is atriarylamine.
 11. A light emitter according to claim 9, wherein the holetransport compound is the4,4′,4″-tris[N-(1-napthyl)-N-phenyl-amino]triphenylamine compound whichhas the formula:


12. A light emitter according to claim 1, wherein the photoalignmentlayer includes a copolymer incorporating both linear rod-likehole-transporting and photoactive side chains.
 13. A light emitteraccording to claim 1, wherein the light emitting polymer is a polymercomprising a light emitting chromophore.
 14. A light emitter accordingto claim 13, wherein the light emitting chromophores is selected fromthe group consisting of fluorene, vinylenephenylene, anthracene andperylene and derivatives thereof and any mixtures thereof.
 15. A lightemitter according to claim 1, wherein the light emitting polymer is aliquid crystal which can be aligned to emit polarised light.
 16. A lightemitter according to claim 1, wherein the light emitting polymercomprises an organic light emitting diode (OLED).
 17. A light emitteraccording to claim 1, wherein the light emitting polymer comprises from5 to 50 monomeric units.
 18. A light emitter according to claim 1,wherein the light emitting polymer comprises uniaxially alignedchromophores.
 19. A light emitter according to claim 1, wherein thelight emitting polymer has a polarization ratio of greater than
 10. 20.A light emitter according to claim 1, wherein the light emitting polymerforms an insoluble, cross-linked network.
 21. A light emitter accordingto claim 1, comprising one or more additional layers of material.
 22. Alight emitter according to claim 21, comprising an electron-transportingpolymer layer.
 23. A light emitter according to claim 22, comprising anelectron transporting polymer of the formula:


24. A light emitter according to claim 1 in pixellated form.
 25. A lightemitter according to claim 24, comprising pixels arranged for polarizedemission.
 26. A light emitter according to claim 24, wherein the pixelsare of the same color but have their polarization direction in differentorientations.
 27. A light emitter according to claim 26, additionallycomprising a photoactive dye as a dopant.
 28. A multicolor light emitteraccording to claim 24, comprising arrangements or sequences of differentpixel colors.
 29. A multicolor light emitter according to claim 28,comprising stripes of red, green and blue pixels having the samepolarization state.
 30. A multicolor light emitter according to claim28, comprising red, green and blue pixels having the same or differentalignment.
 31. A backlight for a display comprising a power input and; alight emitter according to claim
 1. 32. A display comprising a screen;and a light emitter according to claim
 1. 33. A display according toclaim 32, wherein the screen comprises a material selected from thegroup consisting of glass and an organic polymer.
 34. A displayaccording to claim 33, wherein the screen comprises a plastic polymerselected from the group consisting of polyethylene, polyethyleneterephthalate and any mixtures thereof.
 35. An electronic apparatuscomprising a display according to claim
 1. 36. A security viewercomprising a light emitter according to claim 1, wherein the pixels arearranged for polarized emission; and viewing means having a differentpolarization for each eye.
 37. A method of forming a light emitter for adisplay comprising forming a photoalignment layer; aligning a lightemitting polymer on said photoalignment layer.
 38. A method according toclaim 37, additionally comprising forming the light emitting polymer onthe photoalignment layer by an in situ polymerization process.
 39. Amethod according to claim 38, wherein reactive monomer components aredeposited on the photoalignment layer by a spin-coating process.
 40. Amethod according to claim 38, wherein the in situ polymerization processinvolves photopolymerization.
 41. A method according to claim 37,comprising aligning the light emitting polymer by a non-contactphotoalignment method.
 42. A method according to claim 37, additionallycomprising applying an electron-transporting polymer layer.
 43. A methodof forming a multicolor emitter according to claim 37 comprisingapplying a first color light emitter to the photoalignment layer;selectively curing said first color light emitter only where that coloris required; washing off any residue of uncured first color emitter; andrepeating the process for a second and any subsequent light coloremitters.